A standard technique for injection quantity control in fuel injection systems is based on the varying the drive pulse to an actuator in an actuator controlled valve of a fuel injector; i.e. varying the actuator electrical charging time duration. Typically correlation maps between injection quantity and the electrical charging time for various injection pressures over the entire engine operation load map are calibrated in advance and stored in an engine ECU.
With introduction of increasingly tightened emission and CO2 regulations, more precise injection quantity control method is needed. The main demands are to correct injector part-to-part deviation and the injection life-time drift for each injector.
There have been a number of methods and patents published to provide solutions to the above mentioned problem using various techniques. The most simple way is to use the pressure difference value before and after injection as a feedback signal to control the injection quantity, see e.g., US 2010/0199951A1 and US 2014/0216409 A1. This method is based on the principle of fuel compressibility. The injection quantity, namely the quantity released from a closed system with a constant volume, is proportional to the system pressure drop. Such methods can use the existing rail pressure sensor to get the pressure signal for control and thus does not require an additional pressure sensor and no additional modification of the component and system architecture. However, limited by sensor accuracy, ECU resolution accuracy, this method is not accurate enough for low injection quantity control.
For low injection quantity, esp. for pilot injection quantity control, the method based on injection duration is more accurate. For example, DE102011016168 A1 2012-10-11 proposes to detect the needle opening and closing from the solenoid signal. The electric conductivity has a sudden change when the contact status between the needle and the injection nozzle seat changes. This signal change can be used for needle opening (injection start) and needle closing (injection ending) detection. There are several problems with this. If the needle is not strictly co-axial to injector housing during the closing, big detection error can occur and make the control to lose precision. In addition, there is a requirement of expensive seat area coating to avoid life time detection drift caused by seat erosion.
In alternative methodologies pressure sensors are integrated inside an individual injector or alternatively in the fuel passage pipes between the rail and the individual injector. This solution however means that a pressure sensor needs to be utilized for each injector compared to the standard FIE system, and consequently increases the system cost and technical complexity of the injector design.
Patent publications based on injection control by measuring pressure include US 2010/0199951 which uses the rail pressure drop to control fuel injection quantity and US 2014/0216409 which uses rail pressure to control delta quantity of fuel injected.
It is an objective of the invention to overcome these problems.